let div = document.getElementById("div1");
let walker = document.createTreeWalker(div, NodeFilter.SHOW_ELEMENT, null, false);

walker.firstChild();   // go to <p>
walker.nextSibling();  // go to <ul>

let node = walker.firstChild();  // go to first <li>
while (node !== null) {
  console.log(node.tagName);
  node = walker.nextSibling();
}
